CODEWITHSUNDEEP
javacomparecomparatorcomparablecompareto
StyleZ
StyleZ

Reputation: 1273

Collection sort that sort based on class that implements Comparator

I have a problem with Collections sorting, to be more specific

Output:
[B_Author: Movie_X, A_Author: Movie_A, A_Author: Movie_B]
Should Be:
[A_Author: Movie_A, A_Author: Movie_B, B_Author: Movie_X]

method thats supposed to do that (in class MovieStorage):

public Set<Movie> getCatalogue(Comparator<Movie> comp){
        List<Movie> sett = new ArrayList<>(this.movieList);
        sett.sort(comp);
        return new HashSet<>(sett);
    }

Class that implements comparator:

public class MovieComparator implements Comparator<Movie>
{
    @Override
    public int compare(Movie a, Movie b) {
        if (a.getName().compareTo(b.getName()) == 0){
            return a.getAuthor().compareTo(b.getAuthor());
        }
        return a.getName().compareTo(b.getName());
    }
}

called method:

System.out.println(movieStorage.getCatalogue(new MovieComparator()));

I have been looking around StackOverflow and other webs, but I have noticed that everyone sorts it based on 1 parameter ( which doesnt work for me too ) and at a same time, the code is pretty much the same as mine is ...

Thanks for help in advance :)

Upvotes: 0

Views: 107

Answers (1)

boot-and-bonnet
boot-and-bonnet

Reputation: 761

A more compact way to create comparators:

Comparator<Movie> comparator =
    Comparator.comparing(Movie::getName).thenComparing(Movie::getAuthor);

Set<Movie> movies = new TreeSet<>(comparator);
movies.addAll(movieList);

And TreeSet iterates in sorted order.

To add to the Movie class:

public static class Movie implements Comparable<Movie> {
    private static final Comparator<Movie> COMPARATOR =
        Comparator.comparing(Movie::getName).thenComparing(Movie::getAuthor);

    ...

    @Override
    public int compareTo(Movie other) {
        return COMPARATOR.compare(this, other);
    }
}

Then the TreeSet doesn't need a comparator specified:

Set<Movie> movies = new TreeSet<>(movieList);

Upvotes: 2

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